In the field of assaying of complex mixtures of biomolecules, such as protein or nucleic acids, one often uses electrophoresis methods. Especially suitable for this are capillary electrophoresis and isoelectric focusing, but also 2D gel electrophoresis. In recent years, electrophoresis systems in particular have been miniaturized in the form of biochips. This ensures that one can also work with small specimen quantities, the analysis can be highly automated, and the electrophoresis step can be coupled directly to the sample preparation step. This leads to high throughput rates.
In DE 101 13 257 C1 is described an electrophoresis device for analysis of specimens, isolation, purification and preparative recovery of chemical substances, which can be configured as a ready-made miniaturized chip. By means of this chip, one can carry out a two-dimensional electrophoresis. At first, the substances being separated are isoelectrically focused. The pre-separated substances are then separated by capillary gel electrophoresis in second separation channels, arranged perpendicular to the first separation channel.
Two-phase systems are also suitable for protein separation. A protein sample is introduced into a dispersed, generally aqueous two-phase system. Depending on their chemical affinity, the proteins distribute themselves among the different phases. The dispersed phases are then separated after a certain time, making use of the different densities of the two liquid phases. This method is described, e.g., in F. Hachem et al., “Enzyme and Microbial Technology” 19:507-517, 1996.
According to V. G. Gaikar, “J. Chem. Tech. Biotechnol.” 1996, 67, pages 329-332, cationic and anionic surfactant additives are used to support the separation of the proteins. These increase the hydrophobicity of the proteins. A two-phase system based on polyethylene glycol, on the one hand, and sodium sulfate solution, on the other hand, was used. The separating of proteins by means of two-phase, aqueous, surfactant systems was also investigated more closely in C. L. Liu et al., “AIChE Journal”, 1995 Vol. 41, No. 4, pages 991-995.
In V. Reddy et al., “Proceedings of the 7th International Conference on Miniaturized Chemical and Biochemical Analysis Systems”, 5-9 Oct. 2003, Squaw Valley, Calif. USA, pages 437-440, the organic-aqueous liquid extraction based on phenol for the purifying of DNA is described. In order for the individual cell fragments investigated there to be well distributed in the two fluid phases, a two-phase microfluid stream is used, which uses electrodynamic instabilities to enlarge the active surface on which a transition from one phase to the other can occur. The membrane and protein fragments accumulate in the organic phase, while the DNA remains behind in the aqueous phase.
Micromixers are often used for the efficient blending of substances, such as are described, e.g., in T. Herweck et al. “Proceedings of the 5th International Conference on Microreaction Technology, 2001, pages 215-229. Its functional principle is based on the fact that alternatingly arranged, laminar flowing, very thin fluid sheets make possible a mixing of the substances being mixed simply by diffusion.
In S. Devasenathipathy et al., “Proceedings of the 7th International Conference on Miniaturized Chemical and Biochemical Analysis Systems, Oct. 5-9, 2003, Squaw Valley, Calif. USA, pages 845-848, charged colloidal particles in a solution are separated by means of electrokinetic processes. Two buffer streams with different ionic conductivities are introduced into a T-shaped channel system, containing the particles being separated. By applying an electric field, the particles are extracted from the stream with lower conductivity and enriched in the stream with higher conductivity.
In C. W. Theos et al., “Applied Biochemistry and Biotechnology”, Vol. 54, 1995, pages 143-157, under the heading “Electroextraction”, an electrophoretic separation across the phase boundaries is undertaken by applying an electric field to an aqueous two-phase system. Mixtures of two kinds of proteins were separated in a region between isoelectric points, with oppositely charged particles being accumulated in separated phases. The influence of the electrostatic potential on the protein separation in the region of the phase boundaries was investigated at greater length.